Annecy Prosecutor Eric Maillaud told reporters: "This inquiry, which will perhaps not be unique, is the result of evidence collected after the publication on November 4, 2013, of an e-fit of a motorcyclist seen near the scene of the crime and actively sought by investigators."

Last month Mr al-Hilli's brother Zaid al-Hilli, who was arrested in connection with the shooting, had his bail cancelled by Surrey Police after the force deemed there was not enough evidence to charge him with a crime.

The 54-year-old, from Chessington, Surrey, said he was "relieved", but French investigators said they still had "many questions" to ask him.

Since the deaths, speculation has surrounded whether the shooting was linked to the al-Hillis' native Iraq, or Saad al-Hilli's work as a satellite engineer.

Breakthrough: Annecy prosecutor Eric Maillaud (Image: Getty)

Mr Maillaud previously said that police in France were still looking for a motorcyclist seen riding in the area between 3.15pm and 3.40pm shortly before the four murders took place, and a BMW 4x4 also seen there.

The horrific murder scene was discovered by cyclist Brett Martin, who found Iraqi-born Mr al-Hilli and his family massacred in their BMW.

The al-Hilli brothers were alleged to have been locked in an inheritance dispute centred on the £825,000 home in Claygate where Saad and his family lived after their mother died from a heart attack in 2003.

Zaid, who inherited half the property, claimed that in 2011 his brother began to demand his share of the house "there and then" and pinned him down during a row.

The two men never spoke again except through lawyers, but Zaid denied rumours that he had threatened to kill his brother.

He said he knew little about a Swiss bank account containing the proceeds from their father's business in Iraq and would not comment on claims that he attempted to access it using an expired card or tried to fake their father's will.